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    • CommentRowNumber1.
    • CommentAuthorTim_Porter
    • CommentTimeOct 2nd 2018
    • (edited Oct 2nd 2018)

    Added in the usual group presentation of the dihedral group D 2nD_{2n} plus a warning that this group is also denoted D nD_n by some authors (including myself!!!)

    diff, v16, current

    • CommentRowNumber2.
    • CommentAuthorUrs
    • CommentTimeOct 2nd 2018

    Yeah, notation can be a bit of a pain here.

    I have given your remark a remark-environment here, instead of it being a subsection, and edited slightly, mostly for formatting.

    • CommentRowNumber3.
    • CommentAuthorTim_Porter
    • CommentTimeOct 2nd 2018

    Great

    • CommentRowNumber4.
    • CommentAuthorUrs
    • CommentTimeOct 4th 2018
    • (edited Oct 4th 2018)

    added mentioning, pointers, and redirects for “dicyclic group”, synonymous to “binary dihedral group”

    diff, v18, current

    • CommentRowNumber5.
    • CommentAuthorUrs
    • CommentTimeFeb 13th 2019
    • (edited Feb 13th 2019)

    added some actual explicit details on the definition of the binary dihedral groups (here)

    diff, v21, current

    • CommentRowNumber6.
    • CommentAuthorUrs
    • CommentTimeDec 21st 2021

    made explicit (here) the short exact sequence 1/nD 2n/211 \to \mathbb{Z}/n \to D_{2n} \to \mathbb{Z}/2 \to 1.

    diff, v27, current

    • CommentRowNumber7.
    • CommentAuthorUrs
    • CommentTimeJul 6th 2022
    • (edited Jul 6th 2022)

    Is there a citable computation of the group cohomology of dihedral groups with coefficients in \mathbb{Z} equipped with its non-trivial sign action?

    This question is also MO:q/141489.

    I haven’t checked the two answers there yet, but don’t they contradict each other?

    The accepted answer MO:a/141557 sees the cohomology concentrated in odd degrees.

    But the other answer MO:a/141546, whose author claims to have checked this with computer algebra, argues for a nontivial contribution in degree 2.